Touch interface devices can include computing devices having display screens with touch sensitive surfaces that can be used to receive input from operators of the devices. For example, many smart phones, tablet computers, and other devices having touch sensitive screens that identify touches from operators as input to the devices. Other examples of touch interfaces can be found in laptop computers, gaming devices, automobile dashboards, kiosks, operating rooms, factories, automatic tellers, and a host of portable devices such as cameras and phones. Touch interfaces can provide flexible interaction possibilities that discrete controls do not.
“Haptics” refers to the perceptual system associated with touch. Haptics allows people to touch type, find a light switch in the dark, wield a knife and fork, enjoy petting a dog or holding a spouse's hand. Haptics is not just about moving one's hands, but includes perceptions such as feeling things, recognizing objects (even without looking at the objects), and controlling the way that people interact with the world.
Haptics in the form of vibration is a familiar feature of products such as pagers, cell phones, and smart phones. Some known devices use vibration a silent ringer or alarm, and other devices use vibration to provide feedback to the human hand (especially the fingertips) when using a touch screen. Some known touch interface devices use piezoelectric actuators to vibrate just the display screen of the device so that the vibration is felt under the fingertips (e.g., on the screen) and less so or not at all in the hand holding the mobile device (e.g., the vibration is not transmitted through the housing of the device). Such mechanical vibration can have certain drawbacks, such as relatively high energy consumption. Furthermore, such mechanical vibration may not support multitouch, in which multiple fingertips simultaneously or concurrently engage the display screen in more than one location. For example, in some known devices, the entire display screen or even the entire device vibrates. Because the entire screen or device vibrates, each fingertip touching the screen experiences the same effect. As a result, the haptic effects provided to each fingertip cannot be individually controlled (e.g., different from each other) at the same time.
Some other known devices use electrostatic actuation to generate vibrations of the fingertips. These devices use electric fields to apply vibratory forces directly to the fingertips, and therefore do not have any moving mechanical parts. The forces are highly localized and different fingers may in principle experience different forces. These devices, however, produce relatively small forces and can require relatively high voltages (e.g., 750-1000 volts). Moreover, because of the relatively small forces, the devices may be geared toward generating perceived textures only.
What is needed is a system for producing relatively large forces so that not only textures and vibrations, but other effects including virtual bumps, virtual holes, collisions, virtual toggle switches, and the like, can be produced. A need also exists for practical and efficient ways to provide different haptic effects to different fingertips at the same time (e.g., multitouch effects).